【EF Core 】实体映射table-- 实体特性（Data Annonation 标注）&Fluent Api

 

内容来源：https://www.entityframeworktutorial.net/code-first/TimeStamp-dataannotations-attribute-in-code-first.aspx

内容来源：组件模型之数据标注

目录

采用System.ComponentModel.DataAnnotations注解Model的字段

实体特性（Data Annonation  数据标注）： 将实体映射到数据表格。数据标注除了用于数据映射还可以用与数据验证。

Data Annonation & FluentApi
    Data Annonation Attributes

数据映射功能
        Table
        Column
        Key
        NotMapped
        ForeignKey
        Index
        InverseProperty todo

   NotMapped

数据验证功能
        Required
        MaxLength MinLength
        StringLength
        TimeStamp
        DatabaseGenerated
        ConcurrencyCheck
    Fluent Api
        实体映射
        属性映射
————————————————

案例

[Table("StudentInfo")]
public class Student
{
    public Student() { }
        
    [Key]
    public int SID { get; set; }

    [Column("Name", TypeName="text")] //对应数据库的中列
    [MaxLength(20)]
    public string StudentName { get; set; }

    [NotMapped]
    public int? Age { get; set; }
        
    public int StdId { get; set; }

    [ForeignKey("StdId")]
    public virtual Standard Standard { get; set; }
}

 

实体特性（Data Annonation  标注）详解

Table

Table(string name,Properties:[Schema=string])
name:db table name
Schema:要创建的表的架构
如果没有指定些特性，将创建默认的表Students or Studentes
格式：(TableName+‘s’(or ‘es’)
如果指定则按指定的名创建

[Table("StudentInfo")]//将Student实体映射到数据库中的StudentInfo表格
public class Student
{
    
}
using System.ComponentModel.DataAnnotations.Schema;

[Table("StudentMaster", Schema="Admin")]
public class Student
{
    public int StudentID { get; set; }
    public string StudentName { get; set; }
}

 

 

 

Column

[Column(string name,Properties:[Order=int],[TypeName=string])

  • 列名: Name of a column in a db table.
  • 列索引: Order of a column, starting with zero index. (可选)
  • TypeName: Data type of a column. (可选)


索引从0开始，并且不能有重复索引

public class Student
{
    public int StudentID { get; set; }
    
    [Column("Name")]
    public string StudentName { get; set; }
    [Column("DoB", TypeName="DateTime2")]
    public DateTime DateOfBirth { get; set; }
    public byte[] Photo { get; set; }
    public decimal Height { get; set; }
    public float Weight { get; set; }
}

 

 

 

 列的排序

using System.ComponentModel.DataAnnotations.Schema;

public class Student
{
    [Column(Order = 0)]
    public int StudentID { get; set; }
    
    [Column("Name", Order = 1)]
    public string StudentName { get; set; }
    
    [Column("DoB", Order = 5)]
    public DateTime DateOfBirth { get; set; }
    [Column(Order = 3)]
    public byte[] Photo { get; set; }
    [Column(Order = 2)]
    public decimal Height { get; set; }
    [Column(Order = 4)]
    public float Weight { get; set; }
}

 

 

 

 

Key 主键

下面的为组合主键

public class Student
{
    [Key]
    [Column(Order=1)]
    public int StudentId{get;set;}
    [Key]
    [Column(Order=2)]
    public string StudentName
}

ForeignKey 外键

参考

Index 索引

[Index("IndexName,IsClustered=true,IsUnique=true)]
public int OrderNumber{get;set;}

 

Required

必输选项Not Null Column Required

public class Student
{
    public int StudentID { get; set; }
    [Required]//对应的数据库列不能为空null
    public string StudentName { get; set; }
}

 

MaxLength MinLength

C#中对应类型可以string 或 byte[]

using System.ComponentModel.DataAnnotations;
    
public class Student
{
    public int StudentID { get; set; }
    [MaxLength(50)]
    public string StudentName { get; set; }
        
}

 

StringLength

可变长度 nvarchar(50)
[StringLength(50)]
public string Name{get;set;}
public string Name{get;set;}
sqlserver中，将转为数据库中的nvarchar(max)
mysql转为longtext
加上
[MaxLength]转为varchar(50)
[MinLength(50)]转为longtext
[StringLength(50)]也是转为varchar(50) , 

using System.ComponentModel.DataAnnotations;

public class Student
{
    public int StudentID { get; set; }
    [StringLength(50)]
    public string StudentName { get; set; }
}

 

NotMapped 特性

不映射实体的属性到数据库表格中的列。

        [NotMpaaed]
        public string StudentName { get; set; }

        //  此列不会在数据库中创建相关的列。
        ///如果属性只有get或set，也不会创建相关列。如下：
        public int Age { get { return _age; } }
        public double Height { set { _height = value; } }

 

DatabaseGenerated

    • 1.DatabaseGeneratedOption.None
      自己输入值，不用数据库生成的
public class Course
{
    [DatabaseGenerated(DatabaseGeneratedOption.None)]
    public int CourseId { get; set; }
    public string CourseName { get; set; }
}
/* ef core api 中配置
modelBuilder.Entity<Course>()
    .Property(p => p.CourseId)
    .ValueGeneratedNever();
*/

2.DatabaseGeneratedOption.Identity
根据具体的数据库来生成，插入后值不可更新。
有identity rowversion guid 等

public class Course
{
    public int CourseId { get; set; }
    public string CourseName { get; set; }

    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public int RecordNum { get; set; }
}
/* ef core api 
modelBuilder.Entity<Course>().Property(p=>p.CourseId).ValueGeneratedOnAdd();
*/

3.DatabaseGeneratedOption.Computed
在插入或更新的时候来设置值，需要我们自己计算的值

public class Student
{
    public int StudentID { get; set; }
    public string StudentName { get; set; }
    public DateTime? DateOfBirth { get; set; }
    public decimal Height { get; set; }
    public float Weight { get; set; }

    [DatabaseGenerated(DatabaseGeneratedOption.Computed)]
    public DateTime CreatedDate { get; set; }
} 

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    modelBuilder.Entry<Student>().Property(s=>s.CreateDate)
    .HasDefaultValueSql("GETDATE()");
    //这个是调用sqlserver的函数来设置它的值 没有试
}

ConcurrencyCheck

concurrencycheck与timestamp区别
concurrencycheck可用于多个属性的任意数据类型的检测
timestamp只可用于一个byte[]类型属性的检测,一个实体中只可有一个此类型

 public class Student
    {
        [Key]
        public int Sid { get; set; }
        [ConcurrencyCheck]
        public string Sname { get; set; }

        //[Timestamp] mysql中无效
        public byte[] RowVersion;
        public virtual StudentAddress Address { get; set; }
    }

 TimeStamp

一个实体类中只可有一个类型为TimeStamp，用于并发检测
[TimeStamp]，SQLServer中是这样，但是没有装，我也没试。在MySql中，此法无效。需要加入ConCurrencyCheck
public byte[] TimeStamp{get;set;}
参考

在mysql中如果将属性设置为[Timestamp]将报错。
在这里插入图片描述

 

 public class Student
    {
        [Key]
        public int Sid { get; set; }
        [ConcurrencyCheck]
        public string Sname { get; set; }

        //[Timestamp] mysql中无效
        public byte[] RowVersion;
        public virtual StudentAddress Address { get; set; }
    }

 

 

Fluent Api

参考1
参考2
参考3

实体映射

public class SchoolDBContext: DbContext 
{
    public SchoolDBContext(): base("SchoolDBConnectionString") 
    {
    }

    public DbSet<Student> Students { get; set; }
    public DbSet<Standard> Standards { get; set; }
    public DbSet<StudentAddress> StudentAddress { get; set; }
        
    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        //Configure domain classes using modelBuilder here..
        //config default schema
        modelBuilder.HasDefaultSchema("Admin");
        //map entity to table 
        modelBuilder.Entity<Student>().ToTable("StudentInfo");
        modelBuilder.Entit<Student>().ToTable("StandardInfo","dbo");
        
        //map to multiple tables 
        modelBuilder.Entity<Student>().Map(m=>
        {
            m.Properties(p=>new {p.StudentId,p.StudentName});
            m.ToTable("StudentInfo");
        }).Map(m=>
        {
            m.Properties(p=>new {p.StudentId,p.Height,p.Weight,p.Photo});
            m.ToTable("StudentInfoDetail");
        });
        modelBuilder.Entity<Standard>().ToTable("StandardInfo");    
    }
}

 

 

 将一个表分割为2个表

 

也可使用委托或表达式

 

 

 

using System.Data.Entity.ModelConfiguration.Configuration;

namespace CodeFirst_FluentAPI_Tutorials
{
    public class SchoolContext: DbContext 
    {
        public SchoolDBContext(): base() 
        {
        }

        public DbSet<Student> Students { get; set; }
        public DbSet<Standard> Standards { get; set; }
        
        protected override void OnModelCreating(DbModelBuilder modelBuilder)
        {
            modelBuilder.Entity<Student>().Map(delegate(EntityMappingConfiguration<Student> studentConfig)
            {
                studentConfig.Properties(p => new { p.StudentId, p.StudentName });
                studentConfig.ToTable("StudentInfo");
            });

            Action<EntityMappingConfiguration<Student>> studentMapping = m =>
            {
                m.Properties(p => new { p.StudentId, p.Height, p.Weight, p.Photo, p.DateOfBirth });
                m.ToTable("StudentInfoDetail");
            };
            
            modelBuilder.Entity<Student>().Map(studentMapping);
            modelBuilder.Entity<Standard>().ToTable("StandardInfo");
        }
    }
}

属性映射

ublic class SchoolContext: DbContext 
{
    public SchoolDBContext(): base() 
    {
    }

    public DbSet<Student> Students { get; set; }
    public DbSet<Standard> Standards { get; set; }
        
    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        //Configure primary key
        modelBuilder.Entity<Student>().HasKey<int>(s => s.StudentKey);
        modelBuilder.Entity<Standard>().HasKey<int>(s => s.StandardKey);

        //Configure composite primary key
        modelBuilder.Entity<Student>().HasKey<int>(s => new { s.StudentKey, s.StudentName }); 
        
        //config column
        modelBuilder.Entity<Student>()
            .Property(p=>p.DataofBirth)
            .HasColumn("DoB")
            .HasColumnOrder(3)
            .HasColumnType("datetime2")
            .IsOption() //null
            .IsRequired()//not null
            .HasMaxLength(50)
            .HasMaxLength(50).IsFixedLength()//change type from nvarchar to nchar 
            .HasPrecision(2,2) //set size decimal(2,2)
            .IsCurrencyToken()//concurrency check 
            .IsRowVersion()//timestamp type byte[] make it as concurrency column 
            ;
    }
}

 级联删除

EF配置的外键关系除了配置为Optional（可选的，也就是可空），其他默认都是级联删除的，意思就是删除主表的某个数据，相关联的从表数据都自动删除：

 C# 数据类型和对应的SQL Sever数据类型.

C# Data TypeMapping to SQL Server Data Type
int int
string nvarchar(Max)
decimal decimal(18,2)
float real
byte[] varbinary(Max)
datetime datetime
bool bit
byte tinyint
short smallint
long bigint
double float
char No mapping
sbyte No mapping
(throws exception)
object No mapping


 

posted @ 2022-10-14 07:54  小林野夫  阅读(966)  评论(0)  编辑  收藏  举报
原文链接：https://www.cnblogs.com/cdaniu/